The present application claims priority to Japanese Patent Application No. 2001-255866 filed Aug. 27, 2001, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a continuous paper printer that uses the heat roll fusing method, and more particularly, to a continuous paper printer using which stable paper conveyance and printing performance can be obtained without the use of a buffer mechanism that would otherwise be included in order to provide appropriate tension to the continuous paper.
2. Description of the Related Art
Continuous paper printers using the heat roll fusing method have been available in the conventional art, in which folded continuous paper or rolled-up paper is placed in the apparatus and toner images are transferred and fused while the paper is supplied on a continuous basis. The paper conveyance speed provided by the fusing roller is determined in this type of apparatus by the diameter and the rate of rotation, or rpm, of the fusing roller. However, because the fusing roller becomes hot, the diameter thereof fluctuates due to thermal expansion. Therefore, it is difficult to completely match the conveyance speed of the fusing roller to the image conveyance speed of the image formation area. In addition, where continuous paper is used, because the paper is continuous, once a difference arises between the conveyance speed of the fusing roller and the image conveyance speed of the image formation area, such difference accumulates, causing either a gradual increase in the slackening of the paper or the application of excessive tension to the paper.
Accordingly, continuous paper printers equipped with a buffer mechanism that maintains the tension of the continuous paper between the transfer area and the fusing area at an appropriate level are commercially available. Such a continuous paper printer detects the tension of the continuous paper using the buffer mechanism, and by controlling the rate of rotation of the fusing roller in response to the detected tension, an appropriate level of tension is applied to the continuous paper.
A basic construction of a continuous paper printer equipped with a buffer mechanism (so called buffer arm) is shown in FIG. 8. As shown in FIG. 8, a tractor 102 that supplies and conveys continuous paper 101, conveyance rollers 103 and 105, a conveyance motor 112 that drives these components, a conveyance guide 104 and other components are located in the paper supply area of the continuous paper printer. An image forming unit 110 to form toner images on the surface of the photoreceptor drum 107, a transfer roller 106 and other components are located around the photoreceptor drum 107 in the image formation area. The image forming unit 110 includes a charger, an optical system and a developing device. Because the constructions of these components are in the public domain, they will not be described herein.
A fusing roller 108 that performs heat-roller fusing is located in the fusing area, and a paper eject roller 109 is located downstream therefrom in terms of the paper conveyance direction. Here, if the continuous paper 101 were in contact with the fusing roller 108 while the apparatus is standing by for printing, various problems would occur due to the heat supplied to the fusing roller 108, such as burning of the continuous paper. Therefore, in order to avoid such problems, the apparatus is designed such that the fusing roller 108 separates from the continuous paper while the apparatus is standing by for printing.
A buffer arm 116, a suction fan 111 and other components comprising a buffer mechanism are located between the transfer area and the fusing area. A buffer arm detection plate 117 to detect the paper tension is mounted to this buffer arm 116. The rate of rotation of the fusing roller 108 is then controlled based on the tension thus detected. In addition, a buffer arm retracting mechanism (comprising a retracting motor, for example) 115 that retracts the buffer arm 116 downward is connected to the buffer arm 116. Using this buffer arm retracting mechanism 115, when continuous paper 101 is placed in the printer, the buffer arm 116 can be retracted downward, such that after the leading edge of the continuous paper 101 is introduced to the fusing roller 108, the buffer arm 116 is returned to its original position. The suction fan 111 is used to suck the continuous paper 101 onto the buffer arm 116 so that the leading edge of the continuous paper 101 is reliably led to the fusing roller 108 without separating from the buffer arm 116.
In the continuous paper printer described above, the continuous paper 101 is conveyed to the transfer area for the photoreceptor drum 107 via the tractor 102, the conveyance rollers 103 and 105 and the conveyance guide 104. The continuous paper 101 comes into contact with the photoreceptor drum 107 therein, and the toner image on the photoreceptor drum 107 is transferred to the continuous paper 101 by the transfer roller 106. The continuous paper 101 is then conveyed to the fusing roller 108 via the buffer arum 116, whereby the toner image is fused onto the continuous paper 101. The continuous paper 101 is then ejected outside the printer by the paper eject roller 109.
However, the conventional continuous paper printer described above includes a buffer arm 116 between the transfer area and the fusing area in order to supply an appropriate tension to the continuous paper 101. Therefore, the problem of a large apparatus size has arisen. In addition, when the leading edge of the continuous paper 101 is conveyed toward the fusing roller 108, the buffer arm 116 becomes an obstruction. Therefore, in order to avoid this problem, a retracting mechanism 115 by which to temporarily retract the buffer arm 116 downward is also included. As a result, the apparatus also entails the problem of high cost.
These problems can be eliminated by removing the buffer arm 116. However, removing the buffer arm 116 would make it impossible to supply an appropriate tension to the continuous paper 101 between the transfer area and the fusing area. In other words, due to the changes in the rate of rotation of the fusing roller 108, the tension of the paper would fall outside the proper range. If the fusing roller 108 were to pull the continuous paper 101 with an excessive strength, tearing (deformation or ripping of the tracking holes formed on either side of the paper) would occur. It would then become impossible to control the amount by which to convey the continuous paper 101, and the initial printing position on each page would be likely to shift. Conversely, if the continuous paper 101 were too slack, the tension of the continuous paper 101 would become insufficient, resulting in creasing, and a loop would form in the continuous paper 101, resulting in the contact between the unfused toner image and the printer components, which would lead to smudging of the image. As described above, removing the buffer arm 116 would prevent stable conveyance and printing performance from being achieved.
A main object of the present invention is to provide a continuous paper printer by which it is possible, via the provision of an appropriate tension to the continuous paper and the control of the initial printing position, to obtain stable paper conveyance and printing performance without using a buffer mechanism.
In order to resolve the problems identified above, the continuous paper printer pertaining to the present invention has paper conveyance means to supply and convey continuous paper, an image carrier that carries images, transfer means that transfers the image carried on the image carrier to the continuous paper conveyed by the paper conveyance means, fusing means that causes the continuous paper onto which the image has been transferred by the transfer means to pass between rotating units that are mutually in contact, thereby fusing the image on the continuous paper, canceling means that stops the driving of the paper conveyance means after the leading edge of the continuous paper reaches the fusing means, detection means that detects the amount of movement of the continuous paper, and control means that controls the initial image printing position based on the amount of movement detected by the detection means.
In this continuous paper printer, the image on the image carrier is transferred by the transfer means onto the continuous paper supplied and conveyed by the paper conveyance mans, and subsequently, the transferred image is fused onto the paper by the fusing means. Here after the continuous paper is placed in the printer and the leading edge thereof reaches the fusing means, the driving of the paper conveyance means is stopped by the canceling means. In other words, the paper conveyance means comes to move via passive driving. Therefore, the continuous paper thereafter is conveyed at the conveyance speed of the fusing means. Consequently, even when the conveyance speed of the fusing means changes, the continuous paper is pulled with a constant tensile force by the fusing means at all times. Therefore, an appropriate tension can be supplied to the continuous paper at all times without a buffer mechanism. As a result, stable conveyance performance can be obtained. In addition, because no buffer mechanism is included, a retracting mechanism to is not needed, which contributes to making the printer smaller in size and less expensive to manufacture.
However, where the conveyance of the continuous paper is performed by the fusing means, when the conveyance speed of the fusing means fluctuates, the amount of movement of the continuous paper per unit of time fluctuates as well. In addition, because continuous paper is used, such variations in the amount of movement accumulate, causing the initial printing position on each page to shift in a cumulative fashion.
In view of this possible problem, this continuous paper printer detects the amount of movement of the continuous paper via the detection means, and controls via the control means the initial image printing position based on the amount of movement detected by the detection means. Consequently, the initial printing position is reset for each page, so that there will be no accumulated shift in the initial printing position. In other words, even when the conveyance speed of the fusing means changes, there will be no shift in the initial printing position for each page. Therefore, highly stable printing performance can be obtained.
In the continuous paper printer of the present invention, it is preferred that the paper conveyance means include a rotating unit having multiple protrusions that convey the continuous paper, and that the detection means detect the amount of movement of the continuous paper based on the rate of rotation of the rotating unit. Here, the rotating unit may comprise a continuous belt mounted to a tractor, a sprocket, or a grip roller, for example.
By including a rotating unit having multiple protrusions, the paper conveyance means can convey the continuous paper without the paper slipping thereon. Consequently, a proportional relationship results between the rate of rotation of the rotating unit and the amount of movement of the continuous paper. The amount of movement of the continuous paper is then accurately detected by the detection means based on the rate of rotation of the rotating unit. As a result, initial printing position control can be performed with precision.
In addition, it is preferred that the continuous paper printer of the present invention include a guide plate that is located between the transfer means and the fusing means and guides the continuous paper to the fusing means, as this enables the leading edge of the continuous paper to be reliably introduced to the fusing means when the continuous paper is set in the printer.
It is acceptable if an electromagnetic clutch is used for the canceling means that stops the driving of the paper conveyance means.
It is acceptable if more than one paper conveyance means is included. In this case, there may be canceling means for each paper conveyance means to stop the driving thereof. Conversely, it is also acceptable if only specific paper conveyance means have canceling means.
Furthermore, it is acceptable if the control means controls the initial image printing position by changing the timing of issuance of the signal that instructs the initial image printing position.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.